Perfect binding is in widespread use in the publishing business for a wide variety of books. Typically, perfect bound books have a book block comprised of a multiplicity of text pages with a cover adhesively bound to the spine of the book block. The number of text pages comprising the book block may vary considerably, as discussed below. Typically, the cover is of a heavier paper stock (or other suitable material, e.g., a plastic film or the like) than the text pages of the book. Print on demand perfect bound books are now coming into widespread use. Apparatus, such as described in my U.S. Pat. Nos. 6,193,458, 6,443,682 and 7,014,182, and in U.S. Pat. No. 5,465,213, describe known prior art print on demand book publication systems and methods where the resulting books are perfect bound.
As described in my above-noted prior art patents, after the text pages have been printed and accumulated to form a book block, the book block is transported to an adhesive application station where a hot melt adhesive is applied to the spine of the book block. Typically, a reservoir of the adhesive (referred to as a glue pot) is heated to a relatively high temperature, for example ranging between about 325° F. (or lower) and about 375° F. (or higher), depending on the characteristics of the adhesive being used. A rotary driven drum (or wheel) is at least partially submerged in the melted adhesive in the glue pot. As the spine of the book is transported to the adhesive application station, the drum is rotated so as to pick up molten adhesive on the peripheral face of the drum. The drum thus has a coating of the molten adhesive on the periphery of the drum. A wiper bar may be used to wipe off excess adhesive on the periphery of the drum as the latter rotates so as to insure that the layer of adhesive on the face of the drum is of a desired uniform thickness. As the book block is moved past the adhesive application station, the spine of the book contacts (or nearly contacts) the upper reach of the drum and a layer of adhesive is applied to the spine of the book. Such glue pots and rotary drums have been in widespread use in perfect binding systems for many years. While this prior method of applying holt melt adhesive to the spine of the book block in the manufacture of so-called “print on demand” perfect bound books has worked satisfactorily, many disadvantages have been noted, as discussed below.
In the production of a perfect bound book that is printed on demand by apparatus such as shown in my above-noted U.S. patents, it is oftentimes desired that the book be printed and bound within a short time after it is ordered (i.e., commanded to be printed) by the operator or by a customer or even by another computer. If the print on demand apparatus has not been previously warmed up, it will take a considerable time (e.g., 20-50 minutes) to heat the adhesive in the glue pot to a temperature sufficient to properly adhesively bond the book block to the cover. Such a long delay has been objectionable when the glue pot method is employed in a print on demand book printing and binding system. In addition, it has been found that the quality of the binding is quite sensitive to the temperature of the adhesive in the glue pot at the time the adhesive is applied to the spine of the book, to the level of adhesive in the glue pot, and to the length of time that the adhesive has been heated.
It will be appreciated by those of ordinary skill in the art that hot melt adhesives are complex organic chemical mixtures containing compounds of various molecular weights where such compounds may have different melting temperatures and different volatility characteristics. As the adhesive is held at elevated temperatures for extended periods of time, some of the lower molecular weight and more volatile compounds in the adhesive may evaporate thus changing the makeup of the adhesive and changing its ability to properly bond the spine of the book to the cover. Also, as adhesive is consumed in binding of books, additional room temperature adhesive (typically in the form of pellets or small briquettes) must be added to the glue pot. This is typically manually done by the operator. If the level of the molten adhesive in is too low, the rotary drum will not pick up a sufficient layer of adhesive on its face and/or the adhesive may not be sufficiently heated so as to result in a satisfactory binding of the cover to the spine of the book.
Also, because the adhesive in the glue pot is oftentimes kept at its application temperature for extended periods of time, the heated adhesive will tend to give off fumes and/or unpleasant odors. While such fumes and/or odors may not be objectionable in a factory setting, if a print on demand book printing and binding apparatus is utilized in a bookstore or in a library, the emission of such fumes and odors may be problematic. It is also recognized that in an industrial setting, ventilation systems may be used to collect and vent such odors or fumes, but requirement of a special ventilation systems would be difficult and expensive to provide for most print on demand applications.
It has also been found that in order to produce a consistent binding of the book block to the cover the adhesive must wet both the edges of the text pages making up the spine of the book block and a small portion of the face of the outside pages of the book block proximate the spine. This has been difficult to do with the above-described glue pot and rotary drum.
Further in the use of the above-described glue pot and rotary drum, there are many parameters that affect the quality of the binding operation. As noted, the adhesive must be heated to the proper temperature and the quality of the binding is sensitive to adhesive temperature. Thus, the temperature of the adhesive must be maintained within a narrow temperature range (e.g., 350° F., plus or minus 25° F.) of the desired temperature. Also the rotational speed of the drum must be substantially matched to the speed that the book block spine is moved past the drum. If the book spine is moved too fast relative to the surface speed of the drum, a sufficient quantity of adhesive may not be applied to the spine. If the book spine is moved too slowly, excess adhesive may be applied, which may result in the still molten excess adhesive running onto areas of the book block or cover (when the book block is clamped to the cover) as to make an unacceptable book.
In my U.S. Pat. No. 6,142,721, another adhesive application system is disclosed in which a hot melt adhesive is applied while in an unheated or solid state to either to the spine or to the cover in the area that the spine is to be bound to the cover. Then, as the cover is tightly clamped to the spine in close proximity to the spine, an ultrasonic transducer is brought into operative contact with the outside of the cover in the area of the spine and rendered resonant so as to almost instantly heat the adhesive and to effect binding of the cover to the spine of the book block. While this ultrasonic binding method has worked well, such ultrasonic transducer and the required power supply are complex and expensive.
Thus, there has remained a longstanding problem of providing apparatus and a method of utilizing hot melt adhesive for the perfect binding of a book block to a cover in a print on demand book printing and binding apparatus that avoids the above-discussed shortcomings of the prior art.